Such a mechanism is for example described in the specification of published United Kingdom patent application no. GB 2 120 329A, and includes at least one pressure plate, a cover plate, and a diaphragm which is arranged between the cover plate and the pressure plate. The diaphragm bears on the cover plate and on the pressure plate, which is mounted for axial movement with respect to the cover plate, and which is coupled for rotation with respect to the cover plate. The cover plate has a skirt portion and a base portion. The diaphragm biasses the pressure plate towards a reaction plate of the clutch, so as to grip friction liners or pads, carried by a clutch plate of the clutch, between the pressure and reaction plates.
A given clutch mechanism may be used to equip different engines. In that case, only the diaphragm need be a change part, with for example its thickness and/or its inclination being modified as required, in the manner described in the specification of published United Kingdom patent application No. GB 2 011 017A, in order to modify the gripping force of the diaphragm, and to adapt to the torque which is reqired to be transmitted by the engine. In a modification, even the diaphragm is not a change part, being selected so as to carry the highest torque to be transmitted, with the use, where required, of a suitable device to assist the operation, according to the vehicle in which the mechanism is to be installed.
In all case, having regard to the characteristic curve of the diaphragm (which is generally sinusoidal in shape), it can be necessary to use a resilient compensating means. Such a compensating means is described in the above mentioned specification GB No. 2 120 329A, and its purpose is to flatten the characteristic curve of the diaphragm in its working zone, and in particular to reduce the forces required to be exerted by the driver in order to disengage the clutch.
With the arrangements described in GB No. 2 120 329A, there is a problem in that the mechanism has to be pre-equipped with the resilient compensating means, so that it is necessary to differentiate in advance between those mechanisms which must be equipped with such compensating means, and those which need not.